1. Field of the Invention
The present invention relates to a method and a system for controlling power in a portable Internet system, and more particularly to a method and a system for controlling power in a portable Internet system, capable of controlling data transmission output on a mobile communication system by employing an Adaptive Modulation and Coding (Hereinafter, referred to as AMC) scheme using an AMC table including modulation levels of data transmitted on the mobile communication system and request power information according to the modulation levels, together with a power control scheme for additionally applying Bit Error Rate (Hereinafter, referred to as BER) information to the AMC scheme, in a mobile communication network employing the AMC scheme.
2. Description of the Prior Art
With the rapid development of computer, electronic and communication technology, various wireless communication services using a wireless network have been provided. The most basic wireless communication service is a wireless voice communication service for providing voice communication to mobile communication terminal users wirelessly, which has a characteristic of providing the service to the users regardless of time and place. Further, the wireless communication service supplements a voice communication service by providing a text message service. Recently, a wireless Internet service has emerged, which provides an Internet communication service to mobile communication terminal users through a wireless network.
With the development of communication technology as described above, a service provided by a wideband Code Division Multiple Access (Hereinafter, referred to as CDMA) mobile communication system is being developed to a multimedia communication service for the transmission of data such as circuit and packet data, including a conventional voice service.
With the recent development of information communication, an International Mobile Telecommunication (Hereinafter, referred to as IMT)-2000, e.g., a CDMA 2000 1X, 3X, EV-DO and a Wideband CDMA (WCDMA), has been commercialized, which is the 3rd mobile communication system and has been established as a standard by an International Telecommunication Union Recommendation (ITU-R). An IMT-2000 is a service capable of providing a wireless Internet service at a maximum transmission speed of 144 Kbps far faster than 14.4 Kbps or 56 Kbps, which is the data transmission speed supported by an Interim Standard (Hereinafter, referred to as IS)-95A network or an IS-95B network, by means of an IS-95C network evolved from the existing IS-95A network and IS-95B network. In particular, an IMT-2000 service is used, so that the quality of an existing voice and Wireless Application Protocol (WAP) service can be improved and various multimedia services, e.g., Audio On Demand (AOD), Video On Demand (VOD), etc., can be provided at higher speed.
However, because the existing mobile communication system has high base station installation cost, service charges for the wireless Internet are high. Further, because a mobile communication terminal has a small screen, available content is restricted. Therefore, there is a limitation in providing an ultra high-speed wireless Internet service. Furthermore, because Wireless Local Area Network (WLAN) technology shows radio wave interference, narrow service coverage, etc, there is a limitation in providing a public service. Accordingly, a High-speed Portable Internet (Hereinafter, referred to as HPi) system has emerged, which can guarantee portability and mobility and an ultra high-speed wireless Internet service at low cost.
An HPi system uses a 2.3 GHz frequency band, uses a Time Division Duplex (Hereinafter, referred to as TDD) scheme as a duplex scheme, and uses an Orthogonal Frequency Division Multiple Access (Hereinafter, referred to as OFDMA) scheme as an access scheme. Further, an HPi system provides mobility of 60 km/h, which is an Internet Protocol (IP)-based wireless data system having an upload/download asymmetric transmission characteristic in which a download transmission speed is 24.8 Mbps and an upload transmission speed is 5.2 Mbps.
A mobile communication system such as an HPi system has used power control technology in order to use radio resources more efficiently. In particular, the 2nd or 3rd mobile communication system has used high-speed power control technology. This power control technology is technology for controlling transmit power of each mobile communication terminal or transmit power of a base station in order to allow all mobile communication terminals to equally receive services from the same base station. That is, the technology causes a mobile communication terminal having bad channel conditions to consume more transmit power than a mobile communication terminal having relatively good channel conditions, so that transmit signals from all mobile communication terminals can be received in a base station at a constant power level. A base station determines a power value of transmit signals in consideration of channel conditions of each mobile communication terminal, so that all mobile communication terminals can receive signals at a constant power value.
It is usual that a mobile communication system mainly for voice communication employs such power control technology as described above. This is because transfer of better signals beyond the minimum signal intensity necessary for transfer of human voice which does not require a large amount of data is meaningless and may cause excessive battery power consumption which reduce the lifespan of the battery. Further, excessively high signals from one user may cause the resources which can be used by other users to be wasted. Accordingly, the power control technology is used, so that radio wave resources can be preserved. Consequently, services of equal quality are provided to users located in places having unfavorable radio wave conditions and users located in places having favorable radio wave conditions.
A mobile communication system for high-speed packet transmission has used AMC technology in order to allocate radio resources efficiently, in contrast with the 2nd mobile communication system using a fixed coding rate and modulation scheme. Herein, the AMC technology changes the coding rate and the modulation scheme of a mobile communication terminal according to changes in downlink conditions. For this, each mobile communication terminal periodically inspects the downlink conditions and notifies a base station of the inspection result as Channel Quality Information (Hereinafter, referred to as CQI). The base station predicts the downlink conditions for a corresponding mobile communication terminal through the CQI, and designates a proper coding rate and modulation scheme to the corresponding mobile communication terminal based on the predicted downlink conditions. This designation of the coding rate and the modulation scheme is typically performed by an MCS level determined by the CQI. High-speed packet transmission has been proposed as a High Speed Downlink Packet Access (HSDPA) and a 1X-EVDV. A modulation scheme discussed for an AMC in the HSDPA and the 1X-EVDV includes a Quadrature Phase Shift Keying (Hereinafter, referred to as QPSK), a 8PSK, a 16 Quadrature Amplitude Modulation (Hereinafter, referred to as QAM), a 64 QAM, etc., and 1/2, 3/4, . . . , 5/6, etc., are considered as a channel coding rate. Accordingly, a system employing the AMC applies a high order modulation scheme (16 QAM or 64 QAM) and a high coding rate (3/4) to mobile communication terminals using channels of high quality as well as mobile communication terminals near a base station. However, the system typically applies a low order modulation scheme (8 PSK or QPSK) and a low coding rate (1/2) to mobile communication terminals using channels of low quality as well as mobile communication terminals located in a boundary of a cell.
However, both channel conditions and various factors exist in selecting the modulation scheme and the coding rate as described above. That is, even though terminals having the same channel conditions, different modulation schemes and coding rates must be applied to the terminals according to radio wave reflection conditions of surrounding topography, the movement speed of the terminals, changes in inter-cell interference, etc. Further, there is a problem in that a terminal or a base station cannot recognize radio wave conditions of its own channel conditions. Accordingly, a system designer must apply an AMC scheme assuming the worst of these situations. However, this system design may cause a terminal or a base station to output excessive signals in an area having favorable radio wave conditions, thereby increasing interference between system elements. Therefore, the total system capability may deteriorate.